A process of fabricating a flat panel display device or a semiconductor device includes a plurality of thin film deposition processes, photolithography processes for exposing a selected region of the thin film, and processes of etching the selected region of the thin film. In particular, the photolithography process includes a coating process for forming a photosensitive film, which is formed of a photosensitive material, such as a photoresist, on a substrate or a wafer, and exposing and developing processes for patterning the photosensitive film by using a mask having a predetermined pattern. The coating process for forming a photosensitive film on the substrate or the wafer is a spray coating method, a roll coating method, a spin coating method, or the like.
The spray coating method and the roll coating method are not suitable for high accuracy in terms of uniformity of a coating layer and adjustment of layer thickness. The spin coating method is used to form a high-accuracy pattern.
A spin coater as shown in FIG. 1 includes a spin chuck 5 that is connected to a rotary shaft 6, a cover 7 that covers the spin chuck 5 from the outside and can be opened/closed, and a nozzle 4 that is located above the spin chuck 5 and moves inside the cover 7 when the cover 7 is opened.
An object 10 to be coated with a photosensitive film is located on the spin chuck 5. A drain valve (not shown) that drains a photosensitive solution, such as a photoresist, which drops downwards, is installed under the cover 7.
In order for the spin coater to form a coating layer on the object 10, the nozzle 4 moves downwards and jets a photosensitive solution onto the surface of the object 10 that is located on the spin chuck 5. After the photosensitive solution is jetted on the object 10, the cover 7 is tightly closed. A motor M rotates, and the rotary shaft 6 connected to the motor M also rotates, such that the spin chuck 5, on which the object 10 is located, spins at a predetermined rotation rate.
When the spin chuck 5 spins, the photosensitive solution jetted on the upper surface of the object 10 is spread outwards by centrifugal force, such that an entire surface of the object 10 is coated with the photosensitive solution.
When the entire surface of the object 10 is coated with the photosensitive solution, the photosensitive solution is hardened. The hardened photosensitive solution is exposed and developed by using a photo mask or the like, such that a predetermined pattern is formed on the surface of the object 10.
The spin coating method using the spin coater is suitable when a small object, such as a wafer, is coated with a photosensitive solution. When a large and heavy object, such as a substrate for a flat panel display device (e.g., a glass substrate for a liquid crystal display panel) is coated with a photosensitive solution, the spin coating method is not suitable.
The larger and heavier substrate to be coated with a photosensitive film is, the more difficult it is to rotate the substrate at a high speed. In addition, when the substrate is rotated at a high speed, it is much more likely to damage the substrate, and power consumption is also increased.
In addition, a substantial amount of the photosensitive solution is wasted as the amount of photosensitive solution used is much larger than the amount of photosensitive solution that is used for coating. That is, a considerable amount of photosensitive solution coated on the substrate surface scatters out of the spin chuck and wasted when the substrate is rotated at a high speed. In addition, the scatted photosensitive solution tends to act as foreign matter in a subsequent process for forming a thin film, and may contaminate an environment.
Semiconductor flat panel display device fabrication requires photolithography processes in order to pattern a thin film performing a specific function, for example, a metal thin film or a semiconductor thin film to form a predetermined shape. In the photolithography process, a photosensitive material, such as a photoresist that chemically reacts to light, is used.
Defects will be not generated during the process if a photosensitive film is formed to have a very uniform thickness on a substrate on which a thin film is formed. For example, when the photosensitive film is formed to have a greater thickness than a predetermined thickness, a desired portion of the thin film is not etched. In addition, when the photosensitive film is formed to have a smaller thickness than a predetermined thickness, the thin film is etched by a larger amount of etching than a desired amount of etching.
In particular, the uniform coating of the photosensitive solution is a very important factor since the size of the substrate increases in size as a liquid crystal display panel of a liquid crystal display device increases in size.